Green Chemistry in Oscillatory Baffled Reactors - Process Intensification for Green Chemistry - page 167

In addition to the advantages conferred by continuous operation, this reactor was shown
to have higher photon utilization efficiencies than conventional photoreactors and to be less
prone to fouling [9].
5.2.2.1 Green Chemistry Elements
This case study illustrates the following green chemistry principles:
(1) Design for Energy Efficiency: The OBR will be considerably more efficient in terms
of its mixing than comparable conventional technologies for this duty, and this design
is also energy efficient in terms of photon utilization.
(2) Catalysis: This is an excellent illustration of the use of heterogeneous catalysts in
OBRs, and how it can be relatively easily achieved.
5.2.3 'Mesoscale' OBRs
Since 2004, efforts have been ongoing to investigate scale-down of OBRs to 'mesoscale',
referring to OBRs of a fewmillimetres' diameter (typically 4-5mm) [10]. In some areas,
these reactors are referred to as millireactors, but here the prefix 'meso' is used to
distinguish between these and micro- (sub-millimetre diameter) and macroreactors
(the conventional-scale OBRs of 12mm diameter and above). The initial idea behind
this was to facilitate laboratory-scale process development by rapidly producing data
required for scale-up, such as inherent kinetics or mass-transfer information, or else
simply to try out process options in an easily reconfigurable reactor or to determine
process optima.
At mesoscale it is difficult to fabricate geometrically similar baffles to those used
in conventional reactors, as the supports become relatively large, perturbing the flow,
and baffle thicknesses become more important. A number of designs have been developed,
a few of which are shown in Figure 5.10 to give the reader an idea of the variety and scale.
The use of a continuous reactor allows for certain tests to be performed, such as
determination of heterogeneous catalyst lifetime, that would be difficult in batch. The
effect of recycles on the process can also be evaluated. Various designs of continuous flow
screening reactor do exist, but the 'meso-OBR' has some specific advantages:
The ability to suspend solids, whether they are reactants or catalyst particles.
The decoupling of mixing from net velocity allows very long reactions (of the order of
hours) to be performed in continuous mode with plug flow in a reactor of only a few
metres length.
Figure 5.10 Some typical mesoreactor configurations. Reprinted from Phan and Harvey
# 2010, with permission from Elsevier.